A Great Month for Astronomy Enthusiasts

Attention all stargazers! If you haven’t ventured outdoors to do any sky gazing recently, then the astronomical events for the month of December should entice you to do so. Yes, more than likely it is going to be quite cold out in the backyard or an open field, but a well prepared observer would not let that deter him or her from enjoying a couple of great celestial displays. All you’ll have to do is keep yourself warm and the phenomena will reward you for your perseverance.

Have I got your attention? It’s time to get excited about the annual Geminid meteor shower and a total lunar eclipse.

First up is the annual display of meteors known as the Geminids. They are the most consistent of the major meteor shower displays, each year producing 60+ meteors per hour at peak under the best dark sky conditions we have here in southern New England. This year the peak occurs on the night of the 13^th to the early morning of the 14^th. The just past First Quarter Moon will set around midnight, leaving the hours between then and dawns’ early light free of its light and making this the optimum time to observe the most shooting stars.

If you cannot wait until after midnight, the Geminids can be observed early in the evening, unlike some of the other major meteor showers. Why? Gemini, the constellation from where the shooting stars appear to radiate, is about 30 degrees above the eastern horizon by 9:00 pm. (The actual radiant point is very near Gemini’s bright stars Castor and Pollux.) But the moonlight will obscure all but the brightest members of this display early on.

You also do not want to stare directly at Gemini. While you can trace the origin of a Geminids’ trail back to the radiant point, seldom do they begin right at that point in the sky. An observer needs to scan as much of the sky as possible, constantly shifting one’s gaze high and low, right and left.

Standing still out on the cold ground to observe the Geminids gets tiring really fast. While your neighbors might think you have lost your mind, I still suggest you use a lounge chair with a sleeping bag to observe this shower. Dress warmly and simply get comfortable. If there is any wind be sure to block it. I don’t want to hear of any frostbite injuries!

Geminids are fairly bright and moderate in speed, hitting our atmosphere at 21.75-miles per second. They are characterized by their multicolored display (65% being white, 26% yellow, and the remaining 9% blue, red and green). These meteors also have a reputation for producing exploding meteors called fireballs.

Let’s hope the sky gods will smile down upon us for the Geminid meteor shower display on the night of December 13-14. And Mother Nature – no snow please.

The second great astronomical event of December occurs one week later on the morning of December 21. Our geographic location here in New England provides us with an opportunity to observe a total lunar eclipse from start to finish. That’s the good news. The bad news for some is that the eclipse begins here on the east coast at 12:28 am EST and ends at 6:06 am EST, with totality occurring between 2:40 and 3:54 am. It’s a Tuesday morning event, so I suspect there may be a few MIAs at work later in the day.

The only solution would be to book a flight out to the west coast where it will occur three hours earlier. (In Hawaii it occurs before midnight on the 20^th. Anyone planning a trip?) But, if you are going to be stuck at home locally, here’s a brief overview of the event and what you can expect to observe.

A total lunar eclipse occurs when the Sun, Earth and Moon are in alignment. With the Earth placed in the middle of this celestial configuration, its shadow is projected onto the lunar surface. The duration of such an eclipse, particularly of totality, is determined by how precisely the three bodies are aligned.

While the Moon does not pass centrally through the Earth’s shadow during this eclipse (if it did that scenario would produce a long eclipse and longer duration of totality), it does last five hours and 38 seconds from start to finish, with totality lasting one hour and 14 minutes. Though it will take some prime dream time away you, I don’t think many of you can pass up this great viewing opportunity.

Besides, if you carefully review the start and end times of the primary phases of this eclipse, you can easily venture outdoors and catch a few minutes of each phase and then catch a few winks before the next one. However, I’m hoping you will commit a few hours of your time to enjoy this wonderful and beautiful celestial event.

The eclipse technically begins at 12:28 am when the Moon slides into the Earth’s light penumbral shadow. Though this initial phase is undetectable, as the Moon slides deeper into the penumbral shadow a keen-eyed observer will see a subtle shading of the lunar surface. The Moon will be moving eastward as it encounters the shadow, so the left portion of the lunar surface will slowly begin to darken. It is just prior to the Moon entering the Earth's dark umbral shadow that one notices that the moonlight looks somewhat subdued.

When the Moon first encounters the dark umbral shadow at 1:32 am, the partial phase of the eclipse begins. For one hour and eight minutes the Moon will move deeper and deeper into the dark shadow, generally from left to right. Then at 2:40 am the Moon will be completely immersed in the Earth’s dark umbral shadow and totality begins. Totality will last until 3:54 am for a total duration of one hour and 14 minutes. Will the Moon appear to completely disappear from the sky during totality? It all depends upon how much dust is in the Earth’s atmosphere at eclipse time. (With the Iceland volcanic eruption this past Spring and the more recent eruption of Merapi in Indonesia, I suspect totality to be either deep red in color or very dark.) We’ll know by mid-totality at around 3:17 am.

During totality please take careful note of the various hues of color on the lunar surface. Enhance your view with binoculars or a small telescope if you have them. The lunar landscape often looks ashen during totality, with subtle copper, orange or red tones scattered about. And the colors often change as totality progresses. So watch carefully. It is truly a beautiful sight to observe.

Totality ends at 3:54 am when the Moon begins to leave the dark shadow and sunlight returns to its surface. For one hour and eight minutes the partial phase will continue until the entire Moon completely emerges from the dark umbral shadow at 5:02 am. For a while the Moon’s light will still look somewhat subdued as it remains within the light penumbral shadow until 6:06 am when the eclipse ends. (In a dark sky you may be able to detect this shadow soon after the partial phase completes. Thereafter the remaining phase will hardly be noticeable at all as the Moon begins to return to full brightness.)

Please note the sky in the vicinity of the Moon before the eclipse begins. The Moon undergoes its eclipse near the boarder of Gemini, Taurus and Orion. Only a few bright stars will be seen. As the eclipse progresses and the sky becomes darker, watch as the fainter stars emerge into visibility. It will be like someone using a celestial dimmer switch, gradually increasing the brightness of the stars (or if you prefer, decreasing the brightness of the Moon).

I hope the weather will cooperate on the morning of December 21 so that stargazers of every interest level can take advantage of the magnificent circumstances which produce the beauty of a total lunar eclipse. If you miss this one for any reason we won’t experience another total lunar eclipse here in southern New England until April 15, 2014. That’s a long wait, so make every effort to catch a few glimpses of this one to satisfy your love for the beauty nature provides.

Below is a quick-glance chart of the important phases of the December 21, 2010 total lunar eclipse. All times are Eastern Standard Time and are approximate.

Moon enters penumbra (eclipse begins - not detectable): 12:28 am

Moon enters umbra (partial begins): 1:32 am

Moon completely within umbra (totality begins): 2:40 am

Moon nearest to the center of the Earth’s umbral shadow (mid-totality): 3:17 am

Moon begins to leaves umbra (totality ends, partial begins): 3:54 am

Moon completely leaves umbra (partial ends, penumbral begins) 5:02 am

Moon leaves penumbra (eclipse ends - not detectable): 6:06 am

Later that same day the Sun will have reached its most southerly position in our northern hemisphere sky. It’s an event called the Winter Solstice, occurring at 6:38 pm EST. Thank goodness the days will be getting longer once again.

Good luck and keep your eyes to the skies.

And remember, Seagrave Observatory remains open during the winter months unless snow or ice makes the parking lot inaccessible or the grounds impassable. Please visit our web site at http://www.theskyscrapers.org for information. Also, the observatory will be closed on Saturday, December 4.

Should Seagrave be closed, you might visit Ladd Observatory (http://www.brown.edu/Departments/Physics/Ladd/) in Providence. Ladd is open every clear Tuesday night during the winter months from 7-9 pm, weather permitting. Since parking is available on-street, only a parking ban or icy conditions would close the facility. Check out the Ladd website for any cancellations.

Happy holidays and keep your eyes to the skies!